nodes: further optimized merge node to passthrough RGB blend textures

app/render/texture.h

@@ -45,6 +45,19 @@ public:
 
   static const Interpolation kDefaultInterpolation;
 
+  /**
+   * @brief Construct a dummy texture with no renderer backend
+   */
+  Texture(const VideoParams& param) :
+    renderer_(nullptr),
+    params_(param),
+    type_(k2D)
+  {
+  }
+
+  /**
+   * @brief Construct a real texture linked to a renderer backend
+   */
   Texture(Renderer* renderer, const QVariant& native, const VideoParams& param, Type type) :
     renderer_(renderer),
     params_(param),
@@ -67,6 +80,11 @@ public:
 
   void Upload(void* data, int linesize);
 
+  bool IsDummy() const
+  {
+    return !renderer_;
+  }
+
   int width() const
   {
     return params_.effective_width();